1. Field
The present invention relates to magnetic resonance imaging apparatuses, and more particularly magnetic resonance imaging apparatuses that are able to detect the temperature of an imaging space from outside of the imaging space.
2. Description of Related Art
An MRI apparatus detects the radio-frequency signal (NMR signal) that comes from a subject (the patient) by NMR phenomenon. An MRI apparatus applies a gradient magnetic field to the subject to provide spatial information to the NMR signal.
The gradient magnetic field is generated by passing an electric current through a coil to generate the gradient magnetic field. This gradient coil is placed in the direction of the X-axis, Y-axis, and Z-axis in relation to the space coordinates of the subject.
This kind of gradient coil has a large electric current passed therethrough. Therefore, it is problem that the gradient coil develops high heat. Therefore, generally a device for cooling down the gradient coil is set up on the MRI apparatus. Additionally, it has been proposed to provide a temperature sensor that changes its resistance value with a change of temperature, for example a thermoelectric couple and a thermistor, to directly measure the temperature inside of the imaging space in which the gradient magnetic field and the subject are placed (see Jpn. Pat. App. KOKAI Publications No. 04-176440, No. 06-292662).
However, in the case of the related art, the thermoelectric couple and the thermistor detect the change in temperature based on the change in resistance. Therefore, it is necessary to pass an electric current through these sensors. In the case of an MRI apparatus, this electric current generates a noise. Also, in an MRI apparatus the trend of generating high heat on the gradient coils that are placed in the direction of the X-axis, Y-axis, and Z-axis by applying the gradient magnetic field results in a change in temperature at the inside of the imaging space varying through the imaging space. Therefore, a temperature sensor that detects a temperature at a specific point in an imaging space is not completely adapted to be used in an MRI apparatus. Also, a false operation of the temperature sensor and the main device of an MRI apparatus may result by setting up the temperature sensor in the imaging space in that a radio frequency pulse may be applied. Therefore, there are drawbacks with utilizing such a temperature sensor in an MRI apparatus.
For such reasons, the related art systems detecting the temperature in the imaging space may not adequately serve their purpose and may possibly not ensure the safety of the subject and the apparatus.